Production of dimethyl and ethyl thiophenes



Od. 5, 1948. H. E. RAsMussl-:N :a1-A1. l 2,450,637

PRODUCTION 0F DIME'I'HYL` AND ETHYL THIOPHENES Original Filed June 27.14945 PRODUCTION THIOPH EN ES Herbert E. Rasmussen and Rowland chambre, Woodbury, N. J.. assignors to Socony-Vacuum Oil Company, Incorporated, a corporation oi' N ew York Original application June 27, '1945, Serial No. 601,759. Divided and this application August 17, 1946, Serial No. .691,372

This invention relates to the manufacture of alkyl derivatives of thiophene, and is more particularly concerned with a process `for producing alkyl derivatives of thiophene from aliphatic hydrocarbons containing five and six carbon atoms.

Methyl thiophene and dimethyl thiophene as well as thiophene are well known compounds and occur, ordinarily, in the toluene, xylene and benzene fractions, respectively, of coal tar distillates. The amounts of methyl thiophene and of dimethyl thiophene usually present in the crude toluene and xylene fractions respectively, areof the order of about 0.5%. The close proximity of the boiling points of thiophene and benzene, of methyl thiophene and toluene, and of dimethyl thiophene and xylene, renders the complete sep- .aration and recovery of these compounds from the corresponding fractions, by fractional distillatlon, a somewhat difficult operation. Consequently,` commercial benzeneV normally contains traces of thiophene, and commercialtoluene and xylene contain traces of methyl thiophene and of dimethyl thiophene, respectively. However, since thiophene and the alkyl thiophenes are amenable to sulfonation much more readily than benzene, toluene and xylene, thiophene and the alkyl thiophenes can be removed from benzene, toluene and xylene in the form of their sulfonates, by repeated treatments with concentrated sulfuric acid. This. of course, is an expensive operation.

Thiophene has been synthesized in a number of ways. In accordance with the syntheses of the prior art, acetylene has constituted a preferred source of thiophene. Thus, it has been proposed to produce thiophene by reacting acetylene with pyrites, withhydrogen sulfide in the presence oi' catalytic material, with sulfur in the presence or absence oi' catalytic material, and with carbon disulfide. Other syntheses proposed have involved the reaction of other hydrocarbons with sulfur or hydrogen sulfide in the presence of various catalytic materials. Thlophene has been produced also from butyl mercaptan by dehydrogenation and cyclization, by cyclization of other organic compounds. by interchange of heteroatoms in heterocyclic compounds, etc. It must be noted, however, that the yields of thiophene in all of these syntheses generally.. have been uniformly poor, in some cases only traces of thiophene or derivatives thereof being produced.

The inherent chemical character of thiophene and of alkyl derivatives of thiophene, indicates a potentially wide use of these compounds in industrial applications; however, the costly na-v thiophene and alkyl thiophenes from crude benzene, toluene and xylene, and the small yields lof thiophene obtained in the proposed syntheses, lhave somewhat limited the use ci these compounds commercially, the only present outlets of any consequence, being the drug and dye fields.

Various attempts have been made to provide cheap and commercially feasible processes for producing thiophene; but and as noted hereinbefore, 'processes embodying the methods known to the prior art, have suffered from two disadvantages, .the first being the availability and consequently, the cost-of the charging stocks, and the second being the magnitude ol the yields oi' thiophene achieved. Thus, and as is well known to those` familiar with the art, when the charge stock of a given process has been readily available and lits'cost, therefore, has `been relatively low, the yields of thiophene have been small: on the other hand, when the yields have been high, the cost of the charge stock has been high.l

In the Search for readily available and cheap charge stocks to synthesize organic compounds generally, butano and heptane have been reacted wi-th sulfur. These reactions were carried out. to determine what compounds would be formed and not for the express purpose of synf thesizing thiophene or alkyl thiophenes. How- ,'ever, not more than a mere trace of thiophene and no alkyl thiophene were obtained.

Am. Chem. Soc., vol. '51, p. l1566 more normal aliphatic hydrocarbonsl containing l four carbon atoms, to temperatures such that by combining the preheated sulfur and the preheated hydrocarbonmaterial, will give a mixture having a temperature varying between about 850 F. and about 1400 F., mixing the preheated sulfur and hydrocarbon material, maintaining the temperature of the mixture at temperatures in excess of about 850 F. for a period of time of at least about 0.01 second, and reducing the temperature of the mixture to less than about 850 F.

We have discovered that alkyl derivatives oi thiophene may be produced in substantial amounts, by reacting separately preheated aliphatic hydrocarbons containing ve or six carbon atoms, with separately preheated sulfur at elevated temperatures.

"We have now found that methyl thiophene may be obtained by reacting separately preheated aliphatic hydrocarbons containing tive carbon atoms. with separately preheated sulfur at elevated temperatures, and that dimethyl thiophenef ethyl'thiophene and dimethyl thiophene from aliphatic hydrocarbons containing nve and six carbon atoms. A very important obiect is to ailord a process capable ot carrying out the above objects by reacting separately preheated aliphatic hydrocarbons containing. five or six carbon atoms. with separately preheated sulfur at elevated temperatures.

assess? may consist, tor example. in the production o! methyl thiophene, either o! pentane or isopentane or pentenes or isopentenes or even pentadienes. or mixtures oi' them. 0n the other hand, in the manufacture or dimethyl thiophene and/or oi' ethyl thiophene. the aliphatic hydrocarbon charge may consist either of hexane or isohexane or hexenes or isohexenes or even hexadienes, or

mixtures o! them. It should be observed, however. that for economical operation of our process, it is preferred not to use a hydrocarbon charge consisting predominantly of pentadienes or hexadienes because of their tendency to polymerize under the conditions of the process.

An important feature of our invention is that in our process the reaction is highly selective. High yields o! alkyl derivatives of thiophene are obtained. and they may be recovered from the reaction product in a highly pure state using conventional and readily available fractionating equipment.

A very important feature of the present invention is that it provides a cheap and emcient method of producing alkyl derivatives of thioother 'objects and advantages ot the present invention will 'become apparent to those skilled in,

the art from the following description taken in commotion 'with the drawing, in which the single figure represents a diagrammatic illustration of a plant for practicing `the process of our invention. Broadly stated, our invention provides a process for manufacturing alkyl derivatives of thiophene,

' which comprises separately-preheating sulfur and one or more aliphatic hydrocarbons containing five or six carbon atoms, to temperatures such that by combining the sulfur and hydrocarbon materiahwill give a mixture having a temperature inexcess of about 850 F., mixing the preheated sulfur and the preheated hydrocarbon material, reacting the preheated sulfur and the preheated hydrocarbon material at temperatures in excess of about 850 F. for a period of time oi at least about 0.01 second, and reducing the temperature of the mixture to less than about A feature of the process of the present invention is that with the exception of hydrogen suliide, alkyl thiophenes are the principal individual sulfur-containing compounds obtained. A tar. probably a mixture oi complex hydrocarbon polysultldes and/or mercaptans containing about 75% sulfur is also produced. The sulfur in this tar can be recovered and recycled. Carbon disuliide is also formed, but only in small amounts. The hydrogen suliide obtained may be regenerated almost quantitatively back to sulfur for use in the process, by a very inexpensive treatment, such as incomplete combustion into water and sulfur. The sulfur in the tar may be recovered by burning the tar to. produce sulfur dioxide. The sulfur dioxide canthen be reacted with hydrogen sulfide to produce sulfur.

Another feature of the process of the present invention isthat the materials in -the charge, i. e., aliphatic: hydrocarbons containing tive and six .carbon atoms and sulfur. are cheap and plentiful. Generally speaking, any aliphatic hydrocarbon having iive or six carbon atoms and containing at least four carbon atoms in a chain. is suitable-for the process of our invention. The aliphatic hydrocarbons may he derived from any suitable source, as is well known in the art, and

phene. v In our process, n o catalysts are employed. thereby avoiding the disadvantages attendant on their use, such as regeneration and replacement problems, as well as the use of special reaction chambers. The process is substantially a onestep process. although as will subsequently be seen, appreciable amounts of pentenes or hexenes and oi pentadienes'or hexadienes may be found in the effluent from the reaction zone. These may be recycled to the reaction zone for further conversion into alkyl derivatives oi thiophene. thereby increasing the overall yields of the desired products. The equipment required is essentially only a pairof corrosion-resistant alloy preheaters, a corrosion-resistant alloy reactor coil and a corrosion-resistant condensing system. The separation of hydrogen suiiide presents few difiiculties, since most oi?v it can be removed by suitable stabilizing equipment and the last traces removed by caustic scrubbing or other conventional hydrogen sulfide removal processes.

While relatively large quantities of sulfur are employed, it is nevertheless one of the cheapest and most non-critical chemical reagents. We

- have found, in the operation of our process, that the relative proportions oi sulfur and hydrocarbon material may be varied over wide limits. However, too much sulfur results in poor elhciency in sulfur utilization per pass and favors the complete sulfurlzation of hydrocarbon material to carbon disuliide. proportion of sulfur lowers the conversion per pass and the ultimate yield by increasing the overall thermal degradation of hydrocarbon material. Best results are obtained using a weight ratio of sulfur to hydrocarbon material varying between about 0.5 and about 4.0, `although when pentenes or pentadienes, or hexenes or hexadienes constitute the bulk or the hydrocarbon material in the charge, theloweriimit cf the weight ratio may be lower. than 0.5,

The selectivity of the reaction involved in the process of the present invention depends primarily upon two variables. namely, the reaction temperature at which the aliphatic lhydrocarbons containing nve or six carbon atoms are contacted with sulfur, and the reaction time or the time during which contact between the reactants is maintained at the reaction temperature.

The limits of operating temperature are fixed by the kinetics ot the desired reaction and the On the other hand, too low a.

andes?? kinetics of possible side reactions. We have found that the reaction temperature may vary between about 850 F. and about 1300 F., and preferably, between about 900 F. and about 1100 F. Below the lower limit of the temperature range, the reaction is so slow as to require a large throughput of sulfur and a higher ratio of hydrocarbon recycle for a fixed amount of end product, therefore detracting from the economics of the operation. Further. the secondary reaction of tar formation consumes a larger proportion of 'the charge. Above the upper limit of the temperature range, the secondary reaction of degradation of hydrocarbon material in the charge takes precedence, thereby decreasing the yield of desired product. In addition tothis, high temperatures favor the formation of carbon disulfide. It mustbe noted, also, that at these high temperatures.

corrosion problems are at a maximum, corrosionl increasing perceptibly with increasing temperature.

As expected, we have found that the optimum i reaction time depends upon the temperature employed. Generally speaking, other variables remaining constant. the lower the temperature, the longer the reaction time. The reaction or contact time and the reaction temperature are somewhat lxed, one in relation to the other, by the degree of degradation of the hydrocarbon material in the charge, and by the extent of formation of undesirable products, which may be tolerated. Thus. too long a contact time at high temperatures, results in severe cracking of the hydrocarbon material in the charge. The reac- `tion which is highly end'othermic, proceeds with extreme speed, the only limitation apparently beingthe rapidity with which heat can be supplied to the reaction mixture. The lower limit of the range of reaction time is xed, therefore, by the engineering problem of heat transfer and by mechanical limitations such as allowable pressure drop across the reactor. Too long a reaction time at temperatures in the neighborhood of the lower close control of the reaction time at a given reaction temperature. This is very important in the specific reaction producing methyl thiophene or dimethyl thiophene and ethyl thiophene. Without any intention of limiting the scope. of

. the present invention, it is suspected that a` number of reactions occur in the reaction between the hydrocarbon reactant and sulfur. In this connection, the followingshould be noted: cracking of the hydrocarbon reactant destroying the four 'or mce carbon-atom straight-chain structure (the four carbon-atom straight-chain structure limit of the temperature range. results inlower overall yields of alkyl thiophenes dueto increased formation of heavy tar. On the other hand, too short a reaction time at temperatures in the neighborhood of the lower limit of the temperature range, v results' in incomplete reaction. Accordingly, we have found that for best results.

the time of reaction is fixed by the reaction temperature. l

In view of the foregoing, .the criteria to be used in determining optimum operating temperatures within the range 850`1300 F., and reaction times are to choose the degree of conversion desired commensurate with operating cost, such as heat input and equipment costs, bearing' in mind that within limits the shorter the reaction time and Aconcordantly. the higher the temperature, the,

larger the amountA of end product which can be realized from a unit of given size per day.

Generally speaking. the relationship between the temperature of reaction and reaction time is not singular with our invention. It is a well established and fairly well understood relationship in numerous reactions. In the present `instance, we have found that alkyl thiophenes may be produced by reacting sulfur and aliphatic hydrocarbons containing ilve and six carbon atoms at a temperature falling within about 850 F.

and about 1300 F., for a period of time selected to minimize the yield of secondary reaction products at the selected temperature. Accordingly, for the reaction temperature range of our procbeing a prerequisite for the formation of the thiophene nucleus); formation of the thiophene nucleus; formation -of tar high in sulfur; and formation of carbon disulfide. These reactions compete with one another.4 We have found that the rates of the formation of lighter hydrocarb ons and of the formation of carbon dis'uli'lde are somewhat slower than lthat required for theformation of the thiophene nucleus. a proper control of the reaction'time at a given reaction temperature achieved by separate preheating, mixing. heating at a given temperature for a corresponding periodof time, and quenching is necessary to produce high yields of methyl thiophene or ydimethyl thiophene and ethyl thiophene with limited yields of carbon disulfide and fixed gases due to a limited decomposition of the hydrocarbon reactant. The rate of the reaction producing tar is fairly close to that required for the formation of the thiophene nucleus and, therefore, the control of this reaction is more difilcult. Hence, in spite of the separate preheat ing and ultimate quenching of the reaction mixture, the yields of tar approximate those of methyl thiophene or of dimethyl thiophene and ethyl thiophene.

In carrying out the process of the present invention, therefore, it is essential to separatelypre;

heat the reactants. Heating the hydrocarbon material and the sulfur together has two undesirable effects. In the rst place, at 'lower temperatures, the reaction producing tar formationy is the favored reaction; and in the second-place,

our process to separatelypreheat each of the reactants, i. e., the hydrocarbon or the mixture of hydrocarbons constituting the hydrocarbon reactant and sulfur, to such temperatures that when they are brought together, under proper conditions of flow, a temperature falling within the reaction temperature range is achieved, before effecting contact between them. In practice, this is effected ordinarily, by separately preheatlng ess. i. e., 850 F. to 1300 F., when operating con- Accordingly,

assassv each of the reactants to temperatures within the reaction temperature range.

'After the separately preheated hydrocarbon reactant and sulfur are mixed and allowed to re- I Y As stated hereinbeiore, for economical .operation of the process. we prefer not to use a hydrocarbon charge consisting predominantly of penta- `diene or hexadiene, because of their. tendency to polymerize in the preheater with consequent cracking and severe coking in the reactor, However, when pentadiene or hexadiene are used in conjunction with predominant amounts of pentanes and/or pentenes, or with predominant amounts of hexanes and/gr hexenes, respectively, or suitable diluents which are inert with respect to sulfur and to other reaction products of the process. for example. nitrogen, carbon disulfide,

8 must be observed that when pentenes or hexenes are the sole constituents ofthe hydrocarbon reactant, recycling of the hydrocarbons in the eilluent is not commercially feasible in view of the high concentration of pentadienes or hexadienes.

` respectively, in the recycle stock. However. and

l carbon dioxide, etc., they can be processed satisfactorily to give high yields of alkyl derivatives of thiophene. For effective operation of our t process, we have found that pentadienes or hex-y adienes should constitute a minor proportion of the charge.

In our process, the reaction is effected, preferably, at atmospheric pressure or under sumcient pressure to cause the flow of the reactants through the reactor and auxiliary system, under the desired reaction conditions. Tests have shown that the yields per pass and ultimate yields of methyl thiophene or dimethyl thiophene and ethyl thiophene decrease with increase in pressure. However, even at appreciable pressures, methyl thiophene or dimethyl thiophene and ethyl thiophene are nevertheless produced in substantial amounts. Accordingly, there appears to be nothing critical about pressure as a reaction variable. We have found that best results are obtained when turbulent ilow is maintained through the reactor, suitably, a conventional coil-type pipe reactor. With this type of reactor, the desired turbulent tiow may be achieved with a pressure drop of about 1 to 20 pounds across the coil, depending uponthe size of the pipe and the length ofthe coil. Turbulent flow promotes heat-transfer and assures good mixing of the reacting vapors of sulfur and hydrocarbon material.

Recycling of the unreacted portion of hydrocarbon material in the effluent stream, has been found to` be a desirable scheme for increasing the ultimate yield of desired product. This has the same effect as lengthening the reaction time without the attendant and undesirable degradation of hydrocarbon material, referred to Ahereinbefore. When the paraillnic hydrocarbons are the hydrocarbon reactants, it is suspected that the reaction proceeds stepwise with the formation of the corresponding olefini`c hydrocarbons, diolefinic hydrocarbons and'flnally, alkyl thiophenes, each step causing the formation, simultaneously, of hydrogen sulfide, molecular weight for molecular weight. These reactions occur concurrently and unreacted pentane or hexane as well as penas stated hereinbefore. pentanes -or hexanes, or other suitable diluents may be added to the recycle stocks and the latter processed to give high yields of alkyl derivatives of thiophene.

Accordingly. a most important feature of our i process, is that it is flexible. it bein! possible to produce pentenes or hexenes as weily as pentadienes or hexadienes from the pentane or hexane, or pentadienes or hexadienes from pentenes or hxenes, respectively, in addition to alkyl thiop snes.

A plant for practicing the process of our invention with respect to the manufacture of methyl thiophene is illustrated diagrammatically in the drawing. It is understood, of course, that certain modifications of this operating scheme, as well as changes in the type of equipment employed, may be made as long as the essential requirements of the .process are maintained, as will be obvious to those skilled in the art, once the conditions of the process. with which this invention is concerned, are clearly understood. s

Referring now more particularly to the drawing. pentane is pumped from a storage sphere l by a pump l, to a preheater coil l. Molten sulfur is pumped from a storage tank l by a pump I, to a preheater coil 8. The preheated vaporsof pentane and sulfur are mixed at a point l prior to introduction into the reactor, and are then sent through a reactor ooil l. The preheaters 3 and l and the reactor 8 may each be in separate furnaces, as shown, may be of dinerent lengths tb produce the desired preheating temperatures and reaction temperatures. As stated hereinbefore, for economical operation oi' the process of the present invention, short reaction times must be used. This requires rapid mixing of the reactants and rapid heat transfer to the reaction mixture. The reaction products `enter a spray chamber I where they are quenched to a temperature of about 800 ,F..v by spraying suitably with crude methyl thiophene or some other liquid product of the process. The quenched reaction products subsequently are passed into a tar-separator i0, wherein tar separates out and is sent to a sulfurreovery plant i9. The reaction products free of the bulk of the tar. go to a filter i I, to separate the tarmist. A Cottrell precipitator may be used as the mist collector if desired. The filtered products are then passed into a condensate stripper column I-2 where most of the'products that are normally liquid arestripped out. This column may be operated as an absorption stripper by using methyl thiophenebottoms as the absorber liquid. vThe overheadA from the condensate stripper column i2, go to a compressor i3 and thence to a column il where Cs-hydrocarbon gases, gases lighter than Cs-hydrocarbons, and hydrogen sulfide are removed as overhead and sent to the sulfur-recovery plant il. The bottoms lfrom the column il. consisting of (2c-hydrocarbons and materials having boiling points higher than Cs-hy-i tenes or hexenes and pentadienes or hexadienes are found in the eiiluent. Only traces of acetylenic hydrocarbons have been found. The hydrocarbons in the cilluent serve as recycle stream in the recycling operation. In this connection, it

drocarbons, are passed into a column i! where (2f-hydrocarbons are obtained as overhead. The bottoms from column il, consisting of (7s-hydrocarbons and materials having boiling points higher than (Ts-hydrocarbons together with the liquid bottoms from the condensate stripper column i! are passed into a column 2l where f2s-hydrocar- 20 are sent to the carbon disulfide tower Il.

Carbon disulde is taken oi! as overhead from the tower l1 and sent to storage, while the bottoms from the tower Il are passed into a thiophene tower I3 where thiophene produced as aresult of some cracking of C-hydrocarbons into Cl-hydrocarbons, is taken as overhead and to storage. The thiophene tower bottoms are passed finto a methyl thiophene tower I9 where methyl 'thiophene is taken as overhead and to storage and methyl thiophene tower bottoms taken to storage to be used in the condensate stripper column I2 and/or as a spray in the spray chamber 9.

In a typical operation, the hydrocarbon material charged to the preheater coil 6 is made up of a normal pentane cut containing varying amounts of pentenes, obtained from a cracking unit for the conversion of gas oil into gasoline. Sulfur is charged to the preheater 3, in amounts to produce a mixture at 1. having a weight ratio of sulfur to. butane cut, of about 1.0 and the charge rates are adjusted to give v a reaction time of about 0.06 second in the reactor coil 8 at temperatures of The following detailed examples are for the purpose of illustrating modes of producing alkyl thiophenes in accordance with our invention, it being considered as limited to the specific manipulations and conditions set forth hereinafter.

834 grams of isopentane were charged into a preheater at the rate of 40 gramsper minute and heated to-a temperature of 1080 F; 583 grams of sulfur were charged to a separate preheater at a rate of 28 grams per minute and heated to a temperature of 1080 F. The two streams were sent through a mixing nozzle and thence through a baiiled tube reactor of 50 c. c. volume constructed oi' 27% chromium stainless steel maintained at a temperature oi' 1200 F. The reaction product was quenched with a water spray. passed through a small Cottrell precipitator to remove tar mist. and scrubbed through a hot countercurrent caustic tower. The liquid product was cooled, condensed and separated in a water cooler and ice trap. '753 grams oi' liquid were recovered. Frac"- y tionation of the liquid through a 15 theoreticalplatecolumn gave 88 grams of a product having a boiling range of 107-l15 C. Physical measurements and chemical tests established this fraction y to be methyl thiophene.

Example 2 1945. which in turn is a continuation-in-part of copending application, Serial illed September 29. 1944.

The present invention may be embodied in Number 556,438.

other specinc forms without departing from the spirit or .essential attributes thereof. and it is therefore desired that the present embodiments be considered in all respects as illustrative and not restrictive. reference being had to the appended claims rather than to the foregoing description to indicate the scope of the invention.

We claim:

l. A process for producing dimethyl thiophene and ethyl thiophene, which comprises separately preheating sulfur and a hydrocarbon selected from the group consisting oi hexanes. hexenes, and hexadienes. having at least four carbon atoms in a straight chain, to temperatures such that combining said sulfur an'd said hydrocarbon will give a reactionmixture having a temperature varying between about 850 F. and about 1300" F.; mixing the preheated sulfur and the preheated hydrocarbon; reacting said preheated sulfur with said preheated hydrocarbon at a reaction temperature varying between 850 F. and about l300 F. to produce a dimethyl thiophene and ethyl thiophene-containing mixture; and reducing the temperature of said dimethyl thiophene and ethyl thiophene-containing mixture to less than 850 F.

2. A process for producing dimethyl thiophene and ethyl thiophene, which comprises separately preheating sulfur and a hydrocarbon selected from the group consisting of hexanes, hexenes and hexadienes. havingv at least four carbon atoms in a straight chain. to temperatures such that com- -clearly understood that the invention is not to be bining said sulfur and said hydrocarbon will give a reaction mixture having a temperature varying between about 900 F. and about 1100 F.: mixing the preheated sulfur and the preheated `hydrocarbon: reacting said preheated sulfur with said preheated hydrocarbon at a reaction temperaturevarying between about 900 F. and about l100 F. .to produce a dimethyl thiopheneand ethyl thiophene-containing mixture; and reducing the temperature oi said dimethyl thiopheneand ethyl thiophene-containing mixture to less than about 850 F.

3. A process for producing dimethyl thiophene and ethyl thiophene, which comprises separately preheating sulfur and a hexane having at least four carbon atoms in a straight chain. to temperatures such that combining said sulfur and said hexane will give a reaction mixture having a temperature varying between about 850 F. and about l300 F.; mixing the preheated sulfur and "the preheated hexane; reacting said preheated sulfu'r with said preheated hexane at a reaction temperature varying between 350 F. and about 1300 F. for a period of time selected to minimize the yields of hydrocarbons containing less than four carbon atoms per molecule and carbon d isulfide at said reaction temperature, to produce a dimethyl thiopheneand ethyl thiophene-containing mixture; and reducing the temperature of said dimethyl thiopheneand ethyl thiophenecontaining mixture to less than 850 F.

4. A process for producing dimethyl thiophene and ethyl thiophene, which comprises separately preheating sulfur and a hexane having at least four carbon atoms in a straight chain, to temperatures such that combining said sulfur and said hexane will give a reaction mixture having a temperature varying between about 900 F. and about 11001 F.; mixing the preheated sulfur and the preheated hexane; reacting said preheated sulfur with said preheated hexane at a reaction temperature varying between about 900 F. and e minimize the yields of hydrocarbons containing -less than four carbon atoms per molecule and carbon disulfide at said reaction temperature. to produce a dimethyl thiophene and ethyl phene-containing mixture; and reducing the temperature of said dimethyl thiophene and ethyl thiophene-containing mixture to less than about 850 1i.v

5. The process which comprises separately preheating sulfur and a hexane having at least four carbon atoms in a straight chain, to temperatures such that combining said sulfur and said hexane will give a reaction mixture having a temperature varying between about 850 F. and about l300 F.: mixing the preheated sulfur and the preheated hexane; reacting s aid preheated sulfur with said preheated hexane temperature'varying between 850 F. and about 1300 F. for a period oi time selected to minimize the yields of hydrocarbons containing less than four carbon atoms per molecule and carbon di-l suliide at said reaction temperature, to yield a product containing thiophene, methyl thiophene. dimethyl thlophene, ethyl thiophene, normal butane, normal butenes, butadienes, and pentanes. pentenes, pentadienes, hexanes, hexenes and hexadienes, containing at` least four carbon atoms in a straight chain; reducing the temperature of said product to less than 850 F.: separating normal butane, normal butenes. butadienes, and pentanes, pentenes, pentadienes, hexanes, hexenes and hexadienes, containing at least four carbon atoms in a straight chain from said product; and recycling said normal butane, normal butenes, butadienes, and pentanes, pentenes, pentadienes, hexanes, hexenes and hexadienes. containing at least f our carbon atoms in a straight chain to the process.

6. A process for producing dimethyl thiophene and ethyl thiophene, which comprises separately preheating sulfur and a hexene peratures such that combining said sulfur and said hexene will give a reaction mixture having a temperature varying between about 850 F. and about 1300" F.; mixing the preheated sulfur and the preheated hexene; sulfur with said preheated hexene at a reaction temperature varying between 950 F. and about l300 F. for a period ,of time selected to minimize the yields of hydrocarbons containing less than four carbon atoms per molecule and carbon disulilde at said reaction temperature, to produce a dimethyl thiophene-and ethyl thiophene-containing mixture; and reducing the temperature of said dimethyl thiopheneand ethyl thiophenecontaining mixture to less than 850 F.

7. A process for producing dimethyl thiophene and ethyl thiophene, which comprises separately preheating sulfurand a hexene having at least four carbon atoms in a straight chain, to temperatures such that combining said sulfur and said hexene will give a reaction mixture having a temperature varying between about 900 li".v and about l100 F.; mixing the preheated sulfur and the preheated hexene; reacting said preheated sulfur with said preheated hexane at a reaction temperature varying between about 900 F. and about 1100 F. for a period oi time selected to minimize the yields of hydrocarbons containing less than iourcarbon atoms per molecule and carbon disulfide at said reaction temperature, to produce a dimethyl thiophene and ethyl thiophene-containing mixture; and reducing the temperature of said dimethyl thiophene and ethyl at a reaction having vat leastl four carbon atoms in a vstraight chain, to temreacting said preheated thiol2y thiophene-containing mixture to less than about 850 F.

8. The process which comprises separately preheating sulfur and a hexene having at least four carbon atoms in a straight chain, to temperatures such that combining said sulfur and said hexene will give a reaction mixture having a temperature varying between about 850 F. and about 1800 F.; mixing the preheated sulfur and the preheated hexene; reacting said preheated sulfur with said preheated hexane at a reaction temperature varying between 850 F. and about l300'F. for a period of time selected to minimize the yields of hydrocarbons containing less than four carbon atoms per /molecule and carbon disulfide at said reaction temperature, to yield a product containing thiophene, methyl thiophene, dimethyl thiophene; ethyl thiophene, normal butane, normal butenes. butadienes, and pentanes. pentenes, pentadienes, hexanes, hexenes and hexadienes, containing atleast four carbon atoms in a straight chain; reducing the temperature oi' said product to less than 850 F.; separating normal butane, normal butenes, butadienes. and pentanes. pentenes. pentadienes. hexanes, hexenes and hexadienes. containing at least four carbon atoms in a straight chain from said product: and recycling said normal butano, normal butenes, butadienes. and pentanes, pentenes, pentadienes, hexanes, hexenes and hexadienes, containing-at least four carbon atoms in a straight chain to the process.

i 9. A process for producing dimethyl preheating sulfur and a hydrocarbon mixture containing a minor proportion oi.' a hexadiene having at least four carbon atoms in a straight chain. to temperatures such that combining said sulfur and said hydrocarbon mixture will give a reaction mixture having a temperature varying between about 850l F'. and about 1300 F.; mixing the preheated sulfur and the preheated hydrocarbon mixture; reacting said preheated sulfur with said preheated hydrocarbon mixture at a reaction temperature varying between 850 F. and about 1300 F. for a period oi time selected to minimize the yields of hydrocarbons containing less than four carbon atoms per molecule and carbon disuliide at said reaction temperature. to produce a dimethyl thiopheneand ethyl thiophene-containing mixture: and reducingv the temperature of said dimethyl thiopheneand etiyl thiophene-containing mixture to less than 85 F.

i0. A process for producing dimethyl thiolphene and ethyl thiophene, which comprises separately preheating sulfur and a hydrocarbon mixturacontaining a minor proportion oi' a hexadiene having at least four carbon atoms in a straight chain. to temperatures such that combining said sulfur and said hydrocarbon mixture will give a reaction mixture having a temperature varying between about 900 F. and about 1100 F.: mixing the preheated suliur and the preheated hydrocarbon mixture: reacting said preheated sulfur with said preheated hydrocarbon mixture at a reaction temperature varying between about 900 F. and about 1100 F. for a period of time selected to minimize the yields of hydrocarbons containing less than four carbon atoms per molecule and carbon disulfide at said reaction temperature, to produce a dimethyl thiophene and ethylthiophene-containing mixture; and reducing the temperature of said dithiophene and ethyl thiophene, which comprises separatelyv 13, methyl tniophene and ethyl thiophene-containing mixture to less than about 850 F.

11. The process which comprises separately preheating sulfur and va hydrocarbon mixture containing a minor proportion of a hexadiene having at least four carbon atomsin a straight chain. to temperatures such that combining said sulfur and said hydrocarbon mixture will give a reaction mixture having a temperature varying between about 850 F. and about 1300 F.; mixing the preheated sulfur and the preheated hydrocarbon mixture; reacting said preheated sulfur with said preheated hydrocarbon mixture at a reaction temperature varying between 850 F. and about 1300 F. for a period of time selected to minimize the yields of hydrocarbons containingv less than four carbon atoms per molecule and carbon disulfide at said reaction temperature, to yield a product containing thiophene, methyl thiophene, dimethyl thiophene, ethyl thiophene, normal butane, normal butenes, butadienes, and pentanes, pentenes, pentadienes, hexanes, hexen es, and lhexadienes, containing at least four HERBERT E. RASMUSSEN. ROWLAND C. HANSFORD.

REFERENCES orma The following references are of record in the ille of this patent: t

UNITED STATES PATENTs`- Number Name Date 2,389,215 Singleton Nov. 20, 1945 2,410,401 Coffman Oct. 29, 1946 Certificate of Correction Patent No. 2,450,687. October 5, 1948.

HERBERT E. RASMUSSEN ET AL. It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 7, line 7, after the Word below insert about; column 8, line 38, after the syllable naces and before the comma insert j desired, or, if n the same furnaces;

. and that the said Letters Patent should be read With these corrections therein that the same may conform to the record of the case in the Patent O'ce.

Signed and sealed this 10th day of May, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

